When Mother Righteous entered the X-Men's world, no one was sure what kind of impact she would have, let alone her motives or origins. During the events of Mister Sinister's botched timeline, it was revealed that she was deeply tied to him. Initially, Mother Righteous appeared to be a female clone of Mister Sinister, one designed to explore the secrets of magic in an attempt to become a dominion while other Sinister clones pursued other avenues of power.
Source：https://www.cbr.com/xmen-mother-righteous-married-doctor-stasis-mister-sinister/
